(I) Field of the Invention
This invention relates to a method of selectively eliminating a defective zone of a silicon single crystal wafer, and more particularly to a method of forming a nondefective zone in such a wafer by means of heat treatment.
(II) Description of the Prior Art
It is naturally desirable that a silicon wafer used for producing semiconductor devices such as an IC device and an LSI device be nondefective. Crystal dislocations or defects themselves or impurities such as heavy metals gettered by them form a deep level trap center which causes deterioration of semiconductor properties including occurrence of soft breakdown at p-n junctions, decrease of amplification factor and shortening in the life time of minority carrier.
Recently, a method for eliminating such crystal dislocation by heat-treating a silicon single crystal wafer under a non-oxidizig atmosphere has been proposed. According to this method, a wafer is heated at 1,050.degree. C. so as to cause surplus oxygen over the solid solubility limit to precipitate at defect-causing nuclei present within the wafer crystal. As a result, micro defects capable of gettering impurities such as heavy metals are formed in the interior zone of the wafer at a high concentration. On the other hand, oxygen present in the surface region of the wafer and involved in the formation of micro defects is diffused outside the wafer, resulting in formation of a nondefective zone in the wafer surface region. The nondefective zone thus formed is thick enough to form therein an active semiconductor region.
However, rapid progress has been recently achieved in the technique of producing single crystals by improvements in the crucible material, the manufacturing atmosphere, etc., rendering it possible to produce a silicon single crystal which scarcely contains defect-causing nuclei or contains very small nuclei, if present. It has been found that if the prior art outlined above is applied to such a silicon single crystal wafer, micro defects serving to getter impurities such as heavy metals are difficult to form within the wafer. Consequently, the prior art outlined above fails to improve the properties of such a wafer.